# Scaling synapse via workers Synapse has experimental support for splitting out functionality into multiple separate python processes, helping greatly with scalability. These processes are called 'workers', and are (eventually) intended to scale horizontally independently. All of the below is highly experimental and subject to change as Synapse evolves, but documenting it here to help folks needing highly scalable Synapses similar to the one running matrix.org! All processes continue to share the same database instance, and as such, workers only work with postgres based synapse deployments (sharing a single sqlite across multiple processes is a recipe for disaster, plus you should be using postgres anyway if you care about scalability). The workers communicate with the master synapse process via a synapse-specific TCP protocol called 'replication' - analogous to MySQL or Postgres style database replication; feeding a stream of relevant data to the workers so they can be kept in sync with the main synapse process and database state. ## Configuration To make effective use of the workers, you will need to configure an HTTP reverse-proxy such as nginx or haproxy, which will direct incoming requests to the correct worker, or to the main synapse instance. Note that this includes requests made to the federation port. See [reverse_proxy.md](reverse_proxy.md) for information on setting up a reverse proxy. To enable workers, you need to add two replication listeners to the master synapse, e.g.: listeners: # The TCP replication port - port: 9092 bind_address: '127.0.0.1' type: replication # The HTTP replication port - port: 9093 bind_address: '127.0.0.1' type: http resources: - names: [replication] Under **no circumstances** should these replication API listeners be exposed to the public internet; it currently implements no authentication whatsoever and is unencrypted. (Roughly, the TCP port is used for streaming data from the master to the workers, and the HTTP port for the workers to send data to the main synapse process.) You then create a set of configs for the various worker processes. These should be worker configuration files, and should be stored in a dedicated subdirectory, to allow synctl to manipulate them. An additional configuration for the master synapse process will need to be created because the process will not be started automatically. That configuration should look like this: worker_app: synapse.app.homeserver daemonize: true Each worker configuration file inherits the configuration of the main homeserver configuration file. You can then override configuration specific to that worker, e.g. the HTTP listener that it provides (if any); logging configuration; etc. You should minimise the number of overrides though to maintain a usable config. You must specify the type of worker application (`worker_app`). The currently available worker applications are listed below. You must also specify the replication endpoints that it's talking to on the main synapse process. `worker_replication_host` should specify the host of the main synapse, `worker_replication_port` should point to the TCP replication listener port and `worker_replication_http_port` should point to the HTTP replication port. Currently, the `event_creator` and `federation_reader` workers require specifying `worker_replication_http_port`. For instance: worker_app: synapse.app.synchrotron # The replication listener on the synapse to talk to. worker_replication_host: 127.0.0.1 worker_replication_port: 9092 worker_replication_http_port: 9093 worker_listeners: - type: http port: 8083 resources: - names: - client worker_daemonize: True worker_pid_file: /home/matrix/synapse/synchrotron.pid worker_log_config: /home/matrix/synapse/config/synchrotron_log_config.yaml ...is a full configuration for a synchrotron worker instance, which will expose a plain HTTP `/sync` endpoint on port 8083 separately from the `/sync` endpoint provided by the main synapse. Obviously you should configure your reverse-proxy to route the relevant endpoints to the worker (`localhost:8083` in the above example). Finally, to actually run your worker-based synapse, you must pass synctl the -a commandline option to tell it to operate on all the worker configurations found in the given directory, e.g.: synctl -a $CONFIG/workers start Currently one should always restart all workers when restarting or upgrading synapse, unless you explicitly know it's safe not to. For instance, restarting synapse without restarting all the synchrotrons may result in broken typing notifications. To manipulate a specific worker, you pass the -w option to synctl: synctl -w $CONFIG/workers/synchrotron.yaml restart ## Available worker applications ### `synapse.app.pusher` Handles sending push notifications to sygnal and email. Doesn't handle any REST endpoints itself, but you should set `start_pushers: False` in the shared configuration file to stop the main synapse sending these notifications. Note this worker cannot be load-balanced: only one instance should be active. ### `synapse.app.synchrotron` The synchrotron handles `sync` requests from clients. In particular, it can handle REST endpoints matching the following regular expressions: ^/_matrix/client/(v2_alpha|r0)/sync$ ^/_matrix/client/(api/v1|v2_alpha|r0)/events$ ^/_matrix/client/(api/v1|r0)/initialSync$ ^/_matrix/client/(api/v1|r0)/rooms/[^/]+/initialSync$ The above endpoints should all be routed to the synchrotron worker by the reverse-proxy configuration. It is possible to run multiple instances of the synchrotron to scale horizontally. In this case the reverse-proxy should be configured to load-balance across the instances, though it will be more efficient if all requests from a particular user are routed to a single instance. Extracting a userid from the access token is currently left as an exercise for the reader. ### `synapse.app.appservice` Handles sending output traffic to Application Services. Doesn't handle any REST endpoints itself, but you should set `notify_appservices: False` in the shared configuration file to stop the main synapse sending these notifications. Note this worker cannot be load-balanced: only one instance should be active. ### `synapse.app.federation_reader` Handles a subset of federation endpoints. In particular, it can handle REST endpoints matching the following regular expressions: ^/_matrix/federation/v1/event/ ^/_matrix/federation/v1/state/ ^/_matrix/federation/v1/state_ids/ ^/_matrix/federation/v1/backfill/ ^/_matrix/federation/v1/get_missing_events/ ^/_matrix/federation/v1/publicRooms ^/_matrix/federation/v1/query/ ^/_matrix/federation/v1/make_join/ ^/_matrix/federation/v1/make_leave/ ^/_matrix/federation/v1/send_join/ ^/_matrix/federation/v2/send_join/ ^/_matrix/federation/v1/send_leave/ ^/_matrix/federation/v2/send_leave/ ^/_matrix/federation/v1/invite/ ^/_matrix/federation/v2/invite/ ^/_matrix/federation/v1/query_auth/ ^/_matrix/federation/v1/event_auth/ ^/_matrix/federation/v1/exchange_third_party_invite/ ^/_matrix/federation/v1/send/ ^/_matrix/key/v2/query The above endpoints should all be routed to the federation_reader worker by the reverse-proxy configuration. The `^/_matrix/federation/v1/send/` endpoint must only be handled by a single instance. ### `synapse.app.federation_sender` Handles sending federation traffic to other servers. Doesn't handle any REST endpoints itself, but you should set `send_federation: False` in the shared configuration file to stop the main synapse sending this traffic. Note this worker cannot be load-balanced: only one instance should be active. ### `synapse.app.media_repository` Handles the media repository. It can handle all endpoints starting with: /_matrix/media/ ... and the following regular expressions matching media-specific administration APIs: ^/_synapse/admin/v1/purge_media_cache$ ^/_synapse/admin/v1/room/.*/media$ ^/_synapse/admin/v1/quarantine_media/.*$ You should also set `enable_media_repo: False` in the shared configuration file to stop the main synapse running background jobs related to managing the media repository. In the `media_repository` worker configuration file, configure the http listener to expose the `media` resource. For example: ```yaml worker_listeners: - type: http port: 8085 resources: - names: - media ``` Note this worker cannot be load-balanced: only one instance should be active. ### `synapse.app.client_reader` Handles client API endpoints. It can handle REST endpoints matching the following regular expressions: ^/_matrix/client/(api/v1|r0|unstable)/publicRooms$ ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/joined_members$ ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/context/.*$ ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/members$ ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/state$ ^/_matrix/client/(api/v1|r0|unstable)/login$ ^/_matrix/client/(api/v1|r0|unstable)/account/3pid$ ^/_matrix/client/(api/v1|r0|unstable)/keys/query$ ^/_matrix/client/(api/v1|r0|unstable)/keys/changes$ ^/_matrix/client/versions$ ^/_matrix/client/(api/v1|r0|unstable)/voip/turnServer$ Additionally, the following REST endpoints can be handled for GET requests: ^/_matrix/client/(api/v1|r0|unstable)/pushrules/.*$ Additionally, the following REST endpoints can be handled, but all requests must be routed to the same instance: ^/_matrix/client/(r0|unstable)/register$ Pagination requests can also be handled, but all requests with the same path room must be routed to the same instance. Additionally, care must be taken to ensure that the purge history admin API is not used while pagination requests for the room are in flight: ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/messages$ ### `synapse.app.user_dir` Handles searches in the user directory. It can handle REST endpoints matching the following regular expressions: ^/_matrix/client/(api/v1|r0|unstable)/user_directory/search$ ### `synapse.app.frontend_proxy` Proxies some frequently-requested client endpoints to add caching and remove load from the main synapse. It can handle REST endpoints matching the following regular expressions: ^/_matrix/client/(api/v1|r0|unstable)/keys/upload If `use_presence` is False in the homeserver config, it can also handle REST endpoints matching the following regular expressions: ^/_matrix/client/(api/v1|r0|unstable)/presence/[^/]+/status This "stub" presence handler will pass through `GET` request but make the `PUT` effectively a no-op. It will proxy any requests it cannot handle to the main synapse instance. It must therefore be configured with the location of the main instance, via the `worker_main_http_uri` setting in the `frontend_proxy` worker configuration file. For example: worker_main_http_uri: http://127.0.0.1:8008 ### `synapse.app.event_creator` Handles some event creation. It can handle REST endpoints matching: ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/send ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/state/ ^/_matrix/client/(api/v1|r0|unstable)/rooms/.*/(join|invite|leave|ban|unban|kick)$ ^/_matrix/client/(api/v1|r0|unstable)/join/ ^/_matrix/client/(api/v1|r0|unstable)/profile/ It will create events locally and then send them on to the main synapse instance to be persisted and handled.